make "z" toggle between textured mode and wireframe?
It sure is. Just go to Blender's preferences in the Input tab. Search by key-binding: "z". In the 3D View section you will find three "Context Toggle Values" shortcuts, one being assigned to the z key only (no modifier keys). Expand this and change the value of "SOLID" to "TEXTURED".



There is a small yet notable inconsistency in labeling that, in the UI it is listed as "Texture" yet its value name is "TEXTURED" with a D on the end.